https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68483
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |i?86-*-*
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-11-23
Component|other |target
Blocks| |53947
Target Milestone|--- |5.3
Summary|gcc 5.2: suboptimal code |[5/6 Regression] gcc 5.2:
|compared to 4.9 |suboptimal code compared to
| |4.9
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hum, on x86_64 I don't see either GCC 4.9 or GCC 5.2 vectorize the function at
all because they fail to analyze the evolution of the dataref for input[j] as
the initial j of the inner loop is not propagated as zero.
With i?86 I can confirm your observation but I don't see it fixed on trunk.
Note that this boils down to vector shift detection of permutes where (IIRC)
some patterns were not properly guarded on SSE3 support previously and a
wrong-code bug was fixed conservatively on the GCC 5 branch while missing
support was only implemented on trunk.
The failure to vectorize on x86_64 isn't a regression.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
